Cellulose acetates and process of making same.



UNITED STATES PATENT OFFICE.

HENRY DREYFUS, OF BASED, SWITZERLAND.

CELLULOSE ACETATES AND 'ZEROCESS OF MAKING SAME.

No Drawing.

To all whom it may concern:

Be it known that I, HENRY Dnnrrus, a citizen of the'Republic ofSwitzerland, residing at Basel, Switzerland, have invented certain newand useful Improvements in Cellulose-Acetates and Processes of MakingSame, of which the following description is a specification. Y

Y The present invention relates to cellulose acetates having specialproperties, and the methods whereby such acetates are produced.

The known processes of making cellulose acetates mostly depend upon theselection of the particular condensing agent to be employed. The greaterpart of the patents assume that sulfuric acid is highly injurious onaccount of its great splitting action on cellulose. Accordingly varioussubstitutes therefor havebeen proposed,-such as hydrochloric, nitric,nitrosulfuric acids, or salts such aszinc. chlorid, sodiumbisulfate,sulfonic acids, chloracetic acid, etc. In some .iof theseprocesses,'either cellulose or hydro- "cellulose may be employed, 6. 9.that produced by the Girard process, using sulfuric acld of 3% strength,or by using sulfuric and glacial acetic acid. Other processes use moistcellulose to avoid splitting of the cellulose. Each of these processesis said to have 1ts own special advantages, and with the process usingsulfuric acid, etc., -and glacial acetic acid, solutions are obtainedwhich have more or less viscosity, or limpidity, according to the exact.procedure.

The products heretofore produced, have been in nearly all cases solublein chloroform,

and in glacial acetic acid. Films made therefrom have been eitherstretchy, flexible, brittle or otherwise objectionable, rendering thempractically useless, for most purposes.

In my present invention '1 have found a process for thedirectmanufacture, by a direct acetylization process of celluloseacetates insoluble in chloroform,'but soluble in a mixture of chloroformand alcohol, which acetates are also insolublein diluted or concentratedalcohol. Some of these products are soluble in pure acetone, others. aredistinguished by a characteristic behavior upon treating them with pureacetone. They become transparent or semi-fluid'and plastic therein, andby the addition of a small quantity of water, they produce viscoussolutions. In carrying out this process, there Specification of LettersPatent.

Patented May 2, 1916.

Application fi led October 2, 1911. Serial No. 652,442.

is no intermediate stage, in which the cellulose acetates become solublein chloroform. I have found that the manufacture of these productsdepends upon a series of conditions, which must be present in carryingout the reaction. Thus the production of this result depends upon thesimultaneous control, relative to each other, of the tempera tureemployed in the reaction, the humidity or amount of moisture present inthe cellulosic material employed, the amount of condensing agentemployed, the character of the condensing agent employed, and thequantity of acetylating agent relative to the weight of cellulose used.These are some of the factors which are in mutual dependence with eachother, and which" de-. termine the properties of the cellulose. acetatesproduced in carrying out the process. I have found that, in thepreparation of such acetates, sulfuric acid as the convided that certainprecautions are observed,

as follows :1, in carrying out the process at a temperature-not above 40C., and preferably at ordinary room temperature, or by cooling to alower temperature; 2, in employing the proper quantity of theacetylizing agent; 3, in employing the proper quantity of the condensingagent; 4, the amount of moisture in the cellulose or hydrocellulose orpartially acetylized cellulose employed. 1

My new process depends (among other conditions) upon carrying out theprocess of acetylation at or below ordinary room temperature, that is upto about 30 0., and upon employing particular proportions of acetic.anhydrid' or acetyl chlorid, and of sulfuric acid or other condensingagent; both as compared with the amount of cellulose, and also dependinguponthe amount of moisture present in the cellulose, or other cellulosicbody. These conditions depend upon each other. and determine theproperties of'the resulting products. If 10% of sulfuric acid, based onthe weight of cellulose, is used, the amount of acetic anhydrid used canbe varied between 1.5 and 3 kg.

' (preferably 1.8 kg. to 3 kg.) to each kilo to, per kg. of cellulosic.material} there will be used an additional quantity of acetic anhydrid,up to about four times the weight of sulfuric acid used. These figuresare based on using sulfuric acid 95 to 100% strength, pure aceticanhydrid, and cellulose containin 5 to 6% of moisture, and working atordinary room temperature. If the cellulose used contain more or lessthan this amount of moisture, the amount of acetic anhydrid will bein'creasedor diminished accordingly. -Using 10% of sulfuric acid, and 3kg. of acetic anhydrid, per kilo of cellulose containing 5 to 6% ofmoisture and keeping the reacting materials at or below ordinary roomtemperature, products extremely soluble in alcohol-chloroform, butinsoluble in chloroform alone, will be formed, while if dry cellulose,or more acetic anhydrid is used with the same amount of sulfuric acid, aproduct soluble in chloroform will be produced. I have also found thatif it is desired to use a larger amount of sulfuric acid, the amount ofmoisture in the cellulose to be employed should be decreased, otherawise insoluble, pasty or mucilaginous products will be obtained. If 20%or more of sulfuric acid is to be used the cellulose should preferablybe dry, for example cellulose having been dried at 25 to 50 0., in a dryroom, when first treated, as above described, with a mixture of sulfuricand glacial acetic acid. It is not advisable to too much hydrolyze thecellulose-before the introduction I of acetic anhydrid or otheracetylizing agents. Using cellulose containing 5% of moisture it ispreferable to introduce it directly into a mixture of glacial aceticacid, acetic anhydrid and sulfuric acid.

If as much as 25% of sulfuric acid is to be used, dry cellulose shouldpreferably be used, and it should be directly added to the abovedescribed-mixture, otherwise a elatinous product more or lesseasily-solu le in dilute alcohol or hot water will be produced- I havefound, that in order to cause the acetylization to take place in .aregular manner, it is preferable to add the acetic anhydrid, or otheracetylizing agent, to the mixture of glacial acetic acid, sulfuric acidand cellulose, while constantly stirring the reacting mass. For themanufacture,in one.

operatiomof p1x ductshaving a ver.

solubility, the amount .of sulfurib would be between about 10 and 20% ofweight f the cellulose used, .and the above proportlons between thesulfuric acid, moisture content of the cellulose and acetic anhydridshould be rather closely followed. In this manner one can obtainproducts which are capable of producing very concentrated solutions ofcellulose acetates in al ehe ilo eicrm .1 laab at esh a thane and whichcan be used directly in the guished from the cellulose acetatesheretofore'known, by their insolubilit in chloroform and by their greatsolubi ity in alcohol-chloroform.

In order to carry out my'process, dry cellulose, or cellulose with amoisture content of, say about 5%, or cellulose previously treated withdiluted sulfuric acid (and dried down to about 5% of moisture,) orpreferably a cellulose previously treated with a mixture of laclalacetic and sulfuric acids, or a hy ro-cellulose (provided the latter isnot too much decomposed),may be used. It is evident that theafore-mentio'ned. proportions between the moisture content, amount ofsulfuric acid, the amount of acet-ylizin agent and temperature must beclosely fo lowed. By this energetic hydration, that is to say by thepreceding h vdrolization at low temperatures for examp e .ment at lowtemperature is continued for Some time, there is no danger ofdepolymerization of the cellulose -molecule during the acetylizationstep. Also the low temperature at the commencement of the 'acetyli-.zation does not have any disadvantageous grou s have a protectinginfluence upon t cellu ose "molecule. That the hydration at lowtemperatures does have a protecting effect is apparently due to the factthat in the hydration or treatment during and after the introduction ofthe cellulose into the acetyljz-ing mixture at, or preferably below,ordinary room temperature, the temperature does not rise much above thispoint. In accordance with my invention however, I have found that onlythose cellulose acetates which are Subs antially insoluble inchloroform, but which become readily soluble by the addition thereto ofmore or lea alcohol, some of which cellulose acetates are readilysoluble in acetone, and others of which are very soluble in dilutedacetone containing a small amount of water,) are of value fqrtransformation) of rqducts having useful solubiljties, and ot or usefulproperties. These are producedin the present invention,

effect, apparently since the entering acetlyl e in observing theconditions of temperature,

the production, (by further In accordance with my invention, by directlyintroducing the cellulose, and main-" taining the materials at or belowordinary room temperature, unless observing the conditions above pointedout, there will be ob reaction, must in every case be kept down.

In operating in this manner, syrupy liquids are not obtained, butsolutions of the highest viscosity, which do not contain a lar equantity of unchanged fibers, and accor ingly the products produced inaccordance withmy process are transparent, and give in the acetylatingsolution, very viscous products which may even approach a stiff orgelatinous inass. These products and es-.

pecially their transformation products, give solutions of the highestviscosity, which products can therefore be employed in the celluloid andfilm industries.

In order to obtain rapidly a highly viscoussolution, approaching inconsistency a a clear,'stifi gelatinous mass, in accordance with mypresent invention, it is necessary to use very lowtemperatures. Aproduct insoluble in chloroform, together with a high viscosity can beobtained if the temperature is not allowed, even in approaching the endof the acetylation, to approach 40 0., and

. the temperature-duringJ the entire processis preferably kept at orelow ordinary room temperature, to secure the best results. But inconnection with this, I call attention to 'the 'fact that the productsof the present invention are not intermediate productsp'roduced in theprocesses heretofore-employed for the production of chloroform-solublecellulose acetates, since in observing the conditions above stated to benecessary in my process, syrupy solutions will never be obtained. Inmany instances, at the end of the aeetylizing-reaction, there will bepres.-

ent clear, very viscous. solutions, or clear gelatinous massea-pfsuch ahigh viscosity that the arescarcelyinovable or arewholly immova le, thatis say they congeal from their acetylation'solutionaisothat they can 3be pulverized. Such products can 'not be produced if the celluloseisintroduced into an acetylizing mixture having" atemperature at aboveordinary room temperaturei I again call attention to the fact that thepresent invention does notdepend pon'the tem ratureand the ofsulfuricaci alone, but upon these factors in connection with the amountofkmo'i ture in'the 165 employed, andltl S "latter-has to be taken inconsideration.- In a general way the greater the amount of moisturepresent in the cellulose em loyed, the smaller must be the quantity 0condensing agent to be employed, and all the above factors must be keptin mutual dependence one upon the other. In 'using a cellulosecontaining about 5 to 6% of moisture, better results are secured thanwith a dry cellulose, since witha dry cellulose the reaction goes onmuch more slowly, and in connection therewith other inconveniencesresult, for example that theviscosity of thevsolution does not ap earuntilthe last moment, when a clear so ution or clear mass, is obtained.1

.In accordance with my invention it is further necessary to useaquantity of an acetylating agent, such as acetic anhydrid, preferablynot more than three times, and 5 more preferably about two and one-halftimes the weight of the cellulose employed, since the excess ofacetylating agent makes it more diflicult to observe the preferabletemperature, and makes it also more difli-' 90 cult to interrupt thereaction at the proper time. If smaller quantities of sulfuric acid asa'condensing agent have been used, it is easier to regulate thetemperature but the reaction does not go on so energetically. It isalways necessary to employ a certain minimum uantity of sulfuric acid,relatively to 'lulosejintothe acetylating mixture of for example glacialacetic acid, acetic anhydrid, and sulfuric acid, if one employs between10% and 20% of sulfuric acid (and with :advantage not under 5%)calculateduponthe weight of the cellulose employed. In a this oneobtains products, some of .whichar'e easily soluble, in such solvents as5, concmtrated -acetone,'and others in somewha diluted acetone, whichroducts, by

their .ffurther transformation 0 r example in a precipitated form) giyefdther solubili- The products, obtainedi'bymy'prccess are distinguishedin that'while-th'ey are insolubleingchloroform, or in; tetrachlorethanetheylc'anbe dissolved: to" reduce very con-r. centratedsolutionsinalcohol ehloroform, or in alcohol-tetrachlorethane,etc;,;which was not possible with the produ' g heretofore p oduced byany direct he products obtained'in my process are .composed of equalvolumes of the two viously produced, by their great stability which isalso true of the articles made therefrom, by their being substantiallyinsoluble in chloroform, and by their property of being able to givehighly concentrated and viscous solutions of cellulose acetates, inalcohol-chloroform or in alcohol-tetrachlorethane (mixtures of, say,equal volumes of alcohol and chloroform, or alcohol andtetrachlorethane, respectively).

Those products which are completely or partially soluble inalcohol-benzene and other solvents, are of particular interest.

In order to illustrate my invention I give the following examples, theparts being by weight, but it is to be noted that the invention is notlimited to these examples.

Example I: 200 parts of cellulose, for example cotton containing about5% of moisture, are treated with a mixture of 800 parts of glacialacetic acid and 20 parts of concentrated sulfuric acid. Into thismixture,

while constantly stirring, andat ordinary room temperature, or bycooling, 400 parts of acetic anhydrid are slowly added. This additionmay be made at once or after 2 or 3 hours or more. As soon as thematerial dissolves, water may be added, while constantly stirring, toprecipitate the cellulose acetate whichis then washed, pressed, anddried. This product is insoluble in chloroform but swells therein, it issoluble'giving highly concentrated and viscous solutions inalcohol-chloroform or in alcohol-tetrachlorethane, etc., (these solventsfor example being liquids). The product shrinks in pure acetone andforms a transparent, semifluid' I mass which by the addition of a smallamount of water produces a viscous solution, Wlthout preclpitation bywater the solution obtained by acetylization can also be employeddirectly or after neutralization of the mineral acid for the manufactureof artificial silk, or other threads or for other purposes.

Example'II: 200 parts of cotton having a moisture content of about 5%are treated in the'jsame manner with the mixture of 800 parts of glacialacetic acidand '20 partsof concentrated sulfuric acid.- Directly,

or after two'to three hours approximatel 600 parts of acetic anhydridare added,

while constantly stirring and while preventing any substantial rise intemperature, the product is a viscous solution siinilar .to thatproduced in example I which can be worked up in the same manner. Ifdesired the cellulose can also be directly introduced into theacetylizi'ng mixture. The resulting product shows a similar behavior,but in the latter case it may also be soluble in pure acetone.

. Example III 200 parts of dry paper, Such as 1s used in the manufactureof nitrosolving therein. The same remarks apply and after 2 or 3 hours650 to 700 parts of acetic anhydrid are introduced, preferably while themixture is maintained at or below ordinary room temperature, and whilestir ring. A product is obtained similar to that of example II, and isworked up in the same manner.

In these examples, the cotton or paper may be replacedby other forms ofcellulose, or by their products of transformation. Commercial sulfuricacid, glacial acetic acid, and acetic anhydrid can be used, of which thestrength varies more or less or other acetylizing or diluting agents maybe employed.

The proportions of sulfuric acid, lacial acetic acid, acetic anhydrid,and co lulose shouldnot be greatly varied. The amount of moisture in thecellulose may vary somewhat. The cellulose esters may be separated orprecipitated from their solutions in any appropriate manner.

In a very advanced reaction with acetylation solutions, being moremovable or more fluid, the precipitated acetate after drying, becomesfluid in chloroform, without disgenerally to tetrachlorethane, as to choroform, but upon addition of more or less alcohol, either to thechloroform or the tetrachlorethane, the cellulose acetate readilydissolves to produce a viscoussolution, according to the duration of thereaction, and it becomes soluble in concentrated or diluted acetone.These products are insoluble in pure alcohol and in diluted alcohol, andbecome soluble therein, only by the further treatment as per mycopending applications 782,530, filed August 1, 1913, and 73,496.

filed January 21, 1916. What I claim is 1. A process of directlyproducing cellulose acetates substantially insoluble in chloroform', andinsoluble in alcohol, but readily soluble in alcohol-chloroform, whichcomprises reacting upon cellulose with sulfuric acid and acetic anhydridin proportions of about 10 parts of'cellulose, not more than 2% parts ofsulfuric acid, and about 15 to 30 parts of acetic, anhydri'd, at atemperature I not above 40 C.

2. A process of directlfy producing cellulose acetates, insoluble inchloroform and in alcohol, but soluble in chlomform-alcohol, whichcomprises reacting upong cellulose with sulfuric acid and acetic'anhydrid in proportions of about lflparts of moist cellulose, about 1part of sulfuric acid, and about 15 to 30 parts of acetic anhydrid, at atemperature not above room temperature.

- 3. A process-of directly producing celluloseacetate substantiallyinsoluble in chloroform which comprises treating 200 parts of cellulosicmaterial containing about 5% of moisture with a mixture of glacialacetic acid and about 20 parts of sulfuric acid,

then adding, while stirring, and while not above ordinary roomtemperature about 400' parts of acetic anhydrid, then after thecellulose has been transformed into acetateswhich have gone intosolution, precipitating by adding the reaction mixture to Water Whilestirring, separating the precipitated cellulose acetates, and drying thesame.

4. A process of directly preparing celluchloroform and insoluble inalcohol, butwhich are readily. soluble in chloroformalcohol, whichcomprises treating 100 parts of a cellusosic material with a mixtureincluding from 150 to 300 parts of acetic anhydrid and a condensingagent corresponding to about 10 parts of sulfuric acid, said reactionbeing performed at a temperature maintained lower than 40 C. 1

6. -A process of making cellulose acetates which comprises reacting uponcellulose with sulfuric acid and acetic anhydrid in proportions of about10 parts of cellulose, about 1 part of sulfuric acid, and about 15 to 30parts of acetic anhydrid, at a temperature maintained lower than 40-C.,in the presence of a liquid material capable of diluting the liquidreagents employed, but incapable of preventing the acetylizing actionupon the cellulosic material.

7. The process I of making cellulose acev tates substantially insolublein chloroform and in alcohol, but readily soluble in alcoholchloroform,which comprises introducing,

100 parts of cellulose containing about v of moisture into a mixturecontaining glacial acetic acid and about 10 parts. of

concentrated sulfuric acid, and allowing the f materials to react, andthereafter introducing an acetylyzingagent, while the mixture containingthe sulfuric and glacial acetic acids and the acetylizing agent are at atemperature not above ordinary roomtemperature. v

8. A process of producing cellulose acetates, substantially insoluble inchloroform and in alcohol, in, a direct manner, which comprises mixingtogether 800 parts of glacial acetic acid and 20 parts of concentratedsulfuric acid, and introducing thereinto about-200 parts of cellulosecontaining about 5% of moisture, and thereafter adding, whilemaintaining the mixture at not above ordinary room temperature, about400 parts of acetic 'anhydrid.

9. A process of directly producing cellulose acetates substantiallyinsoluble in chloroform and in alcohol, but readily soluble inchloroform-alcohol, which comprises reacting upon cellulose containingnot more than about 6% of moisture with about double its Weight ofacetic anhydrid, in the presence of not more than about 25% of sulfuricacid as a condensing agent, at not above ordinary room temperature 10. Acellulose acetate substantially insoluble in alcohol and in chloroform,but readily soluble in alcohol-chloroform and inalcoholtetrachlorethane, said product being further characterized bygiving upon further treatment with acids, with or without the additionof water, cellulose esters very soluble in acetone.

11. A class of cellulose esters being insoluble in chloroform andinsoluble. in alcohol,

but soluble in alcohol-chloroform, which are further characterized bygiving upon a further treatment with acids or acid salts or mixturesthereof at first cellulose esters soluble. in pure acetone, and which byprolonging the treatment with acids, acid salts or mixtures thereofproduce cellulose esters soluble in dilute acetone and by furtherprolonging finally produce esters soluble in- 12. A cellulose acetateinsoluble in chlor form but soluble in alcohol-chloroform, said productbeing further characterized by giv- I ing upon further treatment withacids, with or without the addition of water, cellulose 1 esters solublein pure acetone, and which by further treatment withv acids giveproducts soluble in water. y

In testimony whereof I have hereunto set my hand in the presence of twosubscribing water.

